Method for non-oxidative production of formaldehyde from methanol

Abstract

Process for the nonoxidative preparation of formaldehyde from methanol The invention relates to a process for preparing formaldehyde from methanol by dehydrogenation in a reactor at temperatures in the range from 300 to 1000° C. in the presence of a catalyst which is introduced into the reactor with the aid of a carrier gas to give a product gas mixture, wherein the formaldehyde is separated from the product gas mixture and at least part of the remaining product gas mixture is recirculated to the reactor in a circulating gas stream and the carrier gas used is a carbon-free gas or gas mixture.

What is claimed is:  
     
       1. A process for preparing formaldehyde from methanol by dehydrogenation in a reactor at temperatures in the range from 300 to 1000° C. in the presence of a catalyst which is introduced into the reactor with the aid of a carrier gas to give a product gas mixture, wherein the formaldehyde is separated from the product gas mixture and at least part of the remaining product gas mixture is recirculated to the reactor in a circulating gas stream and the carrier gas used is a carbon-free gas or gas mixture. 
     
     
       2. The process as claimed in claim  1 , wherein the carbon-free gas is nitrogen or hydrogen or a noble gas or a mixture of these gases. 
     
     
       3. The process as claimed in claim  1 , wherein the amount of carbon-free carrier gas via the catalyst introduction makes up from 1 to 60% of the total gas stream. 
     
     
       4. The process as claimed in claim  1 , wherein the catalyst used is sodium. 
     
     
       5. The process as claimed in claim  1 , wherein the catalyst used is a sodium alkoxide of a lower (C 1 -C 6 ) alcohol. 
     
     
       6. The process as claimed in claim  1 , wherein the reactor is an externally fired tube reactor. 
     
     
       7. The process as claimed in claim  1 , wherein part of the by-products of the dehydrogenation is used for energy recovery or as fuel for heating the reactor. 
     
     
       8. The process as claimed in claim  1 , wherein the hydrogen formed as by-product is separated off and used elsewhere. 
     
     
       9. A process for preparing trioxane, which comprises 
       preparing formaldehyde from methanol by dehydrogenation in a reactor at temperatures in the range from 300 to 1000° C. in the presence of a catalyst which is introduced into the reactor with the aid of a carrier gas to give a product gas mixture from which the formaldehyde is separated off and at least part of the remaining product gas mixture is recirculated to the reactor in a circulating gas stream, wherein the carrier gas used is a carbon-free gas or gas mixture, and  
       trimerizing the formaldehyde obtained in this way to give trioxane.  
     
     
       10. A process for preparing polyoxymethylene, which comprises 
       preparing formaldehyde from methanol by dehydrogenation in a reactor at temperatures in the range from 300 to 1000° C. in the presence of a catalyst which is introduced into the reactor with the aid of a carrier gas to give a product gas mixture from which the formaldehyde is separated off and at least part of the remaining product gas mixture is recirculated to the reactor in a circulating gas stream, wherein the carrier gas used is a carbon-free gas or gas mixture, and  
       optionally, purifying the formaldehyde, and  
       polymerizing the formaldehyde.  
     
     
       11. The process as claimed in claim  2 , wherein the amount of carbon-free carrier gas via the catalyst introduction makes up 1 to 60% of the total gas stream. 
     
     
       12. The process as claimed in claim  11 , wherein the catalyst used in sodium. 
     
     
       13. The process as claimed in claim  11 , wherein the catalyst used is a sodium alkoxide of a lower (C 1 -C 6 ) alcohol. 
     
     
       14. The process as claimed in claim  13 , wherein the reactor is an externally fired tube reactor.